Method for rinsing fabric in a washer and washer adapted to carry out this method

ABSTRACT

A method of rinsing fabric in a washer having a wash chamber rotatable about a horizontal axis comprises the step of adding water to the wash chamber and spraying the rinse water by recirculating it onto the fabric while spinning the wash chamber at a speed to effect a centrifugal force on the fabric such that the fabric will not tumble within the wash chamber as it spins. The method further comprises at least a last rinsing step in which the rotating speed of the wash chamber is such that the fabric tumbles within the wash chamber and in that the rinsing water is not recirculated and sprayed onto the fabric.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of rinsing fabric in a washerhaving a wash chamber rotatable about a horizontal axis comprising thestep of adding water to the wash chamber and spraying the rinse water byrecirculating it onto the fabric while spinning the wash chamber at aspeed to effect a centrifugal force on the fabric such that the fabricwill not tumble within the wash chamber as it spins.

2. Description of the Related Art

The above method is known as “recirculation method” and was designed forreducing water and energy consumption of European domestic washers. Oneof the above methods is disclosed by U.S. Pat. No. 5,191,668.

As a matter of fact water consumption of European domestic washers hascontinuously decreased over the last decades mainly due the cost ofsupply water, the energy cost for heating such water and toenvironmental issues. By introducing a recirculation rinse the wateramount to be used in each rinsing step was greatly reduced, because itwas no longer necessary to have an amount of water sufficient toguarantee wetting of clothes in the drum when tumbling, since the waterwas sprayed on the clothes when these latter were maintained bycentrifugal force against the circular wall of the drum.

On the other hand, beside the actual reduction of water consumption,consumers are increasingly complaining about laundry feeling soapy afterwash, laundry crackling with foam residual after wash, spots ofinsoluble compounds (zeolites) on the laundry, and eczema from residualdetergent on the fabric.

All the above negative effects are mainly due to a too high residualconcentration of detergent in the rinsing water (including zeolitesusually contained in detergent formulations), to laundry fluff, tochunky food particles, to sand and rust articles from plumbing. Allthese substances are brought back onto the clothes throughrecirculation. Therefore recirculation is rarely implemented in modernwashers mainly because of added cost of parts, difficulty to drawbenefit from it because specific cycle layout is required to avoiddrawback of soil/detergent redeposition on laundry and drawback of suds.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method as stated atthe beginning of the description that does not have the above drawbacks,while keeping water consumption comparable to that of the recirculationmethod already known.

According to the invention, the above object is reached thanks to thefeatures listed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention will now be described by way ofexample with reference to the attached drawing, wherein:

FIG. 1 is a time chart of the rinse cycle of a washing machine accordingto a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The applicant has surprisingly discovered that by slightly modifying theknown recirculation rinse method it is possible to avoid the aboveproblems, while maintaining a good rinsing efficiency and a reducedconsumption of water.

The preferred method according to the invention comprises a final rinsewhere water is no longer recirculated and sprayed on the clothes, whileclothes are tumbled in an increased amount of rinsing water compared tothe previous rinsing step in which recirculation of rinsing water wascarried out. If for instance there are three rinse cycles, therecirculation of water will be carried out in the second rinse andoptionally also in the first one, but not in the last one where theamount of used rinsing water will be higher than that of the previouscycle. The rinse with recirculation can be done with a small wateramount, typically 5 litres for a load of 5 kg of laundry instead of anormal amount of about 10 litres. During rinsing the water is pressedthrough the laundry by acceleration of the drum until the laundry formsa ring on the drum surface. The recirculated water is sprayed onto thelaundry ring to achieve good distribution of the water through thelaundry. With the term “sprayed” we mean every possible way in which thewater is fed onto the laundry ring, independently on the way it is fed,either by gravity or by a water nozzle under water pressure.

Preferably, the drum is slowed down to normal tumbling movement to allowthe rinsing water (which is continued to be sprayed) to access fibres oflaundry in an uncompressed state. Preferably the rotation of the drum isreversed between the spinning step and the tumbling step. The process ofrecirculating and accelerating the drum can be repeated several timesuntil the rinsing water is saturated with detergent. The washing machineaccording to the invention is preferably provided with a sensor(turbidity sensor, capacitive detergent concentration sensor, andconductivity sensor) which is capable of detecting when the rinsingwater is substantially saturated with detergent. The same sensor can beused in order to assess the optimal number of rinsing cycles. The lastrinse cycle is done with a normal tumbling movement, no recirculation,and an increased water amount since water has been saved in the previousrinse cycles.

The spinning speed of each rinsing cycle depends on the drum diameter,and it is preferably of about 80 to 85 rpm for approximately 548 mm drumdiameter or of about 65 to 75 rpm for approximately 480 mm drumdiameter. Centrifugal force must be strong enough so that laundry stopsits tumbling movement inside the drum. Laundry must form a ring clingingto the inner drum wall, but speed must be safely below “critical speed”.“Critical speed” is the speed corresponding to the resonance frequencyof the wash unit. Every time the appliance goes through critical speed,there is strong noise and vibration. Appliance lifetime is shortened ifit goes through critical speed often. Moreover speed should be as low aspossible to avoid excessive suds creation. Excessive suds leads to badrinse performance, difficult draining at the end of the rinse cycle and,in the worst case, oversudsing of appliance, with suds being pressedoutside through the soap dispenser.

According to the tests performed by the applicant, the number of“accelerate+recirculate” repeats is preferably comprised between around2 and 12 in order to achieve saturation of liquor with detergent, whereabout 12 repeats are used in case of large soakable washload (in washerdrums having a diameter of about 548 mm) with high dosage ofhigh-foaming detergent, and where about 2 repeats are used with smallload (up to approx. 15% of rated capacity) and moderate dosage oflow-foaming detergent.

Load amount/soakability can be detected by measuring motor torque inacceleration ramp and use flowmeter to measure water amount, or bymeasuring gradient of water take-up (water level decrease after filling)with analogue level sensor. Foaming can be detected with analogue levelsensor or optical (turbidity) sensors.

Even if an “accelerate+recirculate” methodology of rinsing is thepreferred one, permanent recirculation without any slowing down can beused for small loads.

In order to determine when we have achieved saturation of the rinsewater with detergent, it is possible to use either a lookup tablelinking the number of “accelerate+recirculate” repeats with the detectedload amount/soakability and/or the presence or absence of foam, or asensor (of the type already mentioned) to detect when the detergentconcentration stays near-constant from one repeat to the next.

The recirculation system has the advantage that such a sensor can bemounted to the tub outlet or recirculation hose. In an appliance withoutrecirculation, rinse sensors must be mounted to the tub wall. This isexpensive and often reduces stability of the tub (turbidity sensor needshole in tub wall with several cm diameter).

The design of a washing machine according to the present inventionimplies that highly concentrated liquor is recirculated. There istherefore a high risk of suds creation in such a design.

There is also a high risk of water ring. “Water ring” means that whilethe drum is spinning, the water that is pressed out through the drumholes cannot be drained off by the pump fast enough. Therefore it formsa rotating ring at the outside of the drum, leading to bad draining,noise, and vibration of the machine. This happens when a water-saturatedlarge soakable load is accelerated to high speeds too fast, or thedraining rate of the drain pump is too low since the pump is too weak orthe pump is blocked with foam, fluff or foreign bodies (buttons, coins),or the outlet geometry is unsuitable.

To solve the above problems while keeping a low cost of therecirculation pump, it is suitable to apply a pump with around 4 l/minto 6 l/min draining rate for a sump (free liquor) volume of around 4 l.

Moreover, a fluff filter and foreign body trap is incorporated in thebody of the drain pump. Further features and advantages of a rinsemethod according to the present invention will be clear from thefollowing detailed description, given by way of non limiting example,with reference to the attached drawing which shows a speed profile ofthe last two rinse cycles according to the present invention, togetherwith the recirculation pump status (on/off) and with the total supply offresh water to the tub.

With reference to the upper part of the drawing, on the y-axis isreported the drum speed, while in the intermediate and lower part of thedrawing the status of the recirculation pump and the loaded water arereported respectively. On x-axis time is reported. On the left portionof the diagram (last but one rinse cycle), with an amount w1 of rinsingwater the drum speed is changed from s1 (tumbling speed) to s2 tumblingspeed for two times. Between recirculation phases (times t1 and t2) thedrum is tumbled without recirculation and with inverted direction. Thismeans that the drum is rotated in alternating directions: at speed s1counterclockwise for some seconds and, after a pause of some seconds, atspeed s1 clockwise for some seconds. At time t3, after and intermediatespin for removing rinse water from clothes, the drum is stopped, therinsing water w1 is pumped out and fresh water is added to the tub, sothat at time t4 the total water loaded in the tub in the last two rinsecycles is w2 (where added fresh water in the last rinse cycle is w2−w1,which is higher than w1). Then the drum is rotated at tumbling speed s1(last rinsing cycle) in alternating directions up to time t5 when wateris pumped out and the final spinning cycle is started.

Another further advantage of recirculated rinse according to the presentinvention is that in case of warm rinse (often applied in washers soldin US), the recirculated water can transfer the heat of the inlet rinsewater to the laundry. Heat distribution is therefore more even and theheat of the inlet water is reaching the laundry surface much faster thanin traditional rinsing. Thus the desired rinse result can be reachedfaster.

1. A method of rinsing fabric in a washer having a wash chamberrotatable about a horizontal axis comprising: the step of adding waterto the wash chamber and spraying the rinse water by recirculating itonto the fabric while spinning the wash chamber at a speed to effect acentrifugal force on the fabric such that the fabric will not tumblewithin the wash chamber as it spins, wherein that it comprises at leasta last rinsing step in which the rotating speed of the wash chamber issuch that the fabric tumbles within the wash chamber and in that therinsing water is not recirculated and sprayed onto the fabric.
 2. Themethod according to claim 1, wherein the water amount added in the lastrinsing step is higher than the water amount used in the previousrinsing steps.
 3. The method according to claim 1, wherein that in eachrinsing step with recirculation of rinsing water the washing chamber isaccelerated to the speed to effect a centrifugal force on the fabric andit is then slowed down in order to allow tumbling of the fabric, suchalternating acceleration and slowing down being repeated several timesin each rinsing step.
 4. The method according to claim 3, wherein thealternating sequence of acceleration and slowing down of the washchamber is repeated from about 2 to 12 times.
 5. The method according toclaim 3, wherein it comprises detecting the detergent concentration inthe rinsing water, the last rinsing step being carried out when suchdetergent concentration is lower than a predetermined value.